Never. When the next WHQL driver comes out (probably not this month), it will be numbered after the year.month sematic as usual. So if it comes in september, it'll be 13.9. If it comes in december, it'll be 13.12 etc.

Why are you afraid of non-WHQL drivers? They work the same way, you only get a warning from the OS when you install the package. That's all.